I received this rely a few years ago but never posted it. I had written to Queen Paola for her birthday.
The envelope is one of the usual used from Belvédère, featuring a purple crown with the word Belvédère underneath to match the card.
The reply is the usual flat card, although the message will vary each year. The faded print of the card is how I received it.
The reply says:
Belvedere
Her Majesty Queen Paola thanks you wholeheartedly for the kind wishes sent on the occasion of her 83rd Birthday
September 2020